DESCRIPTION: A-cells in the pancreatic islets release glucagon in response to amino acids; this response is subject to inhibition by glucose. The glucose- dependent regulation of glucagon release is impaired in type 1 and in type II diabetic patients. Compared to B-cells, little is known about stimulus- secretion coupling in glucagon-secreting A-cells. This proposal is broadly aimed at filling this gap. The central hypothesis to be tested is that A- cells (which are fuel-sensitive) contain ATP -sensitive K+-channels and that these channels regulate glucagon release as a function of the extracellular concentration of amino acids and glucose. To test this hypothesis, biochemical and electrophysiological techniques will be used with single normal A-cells prepared by fluorescence-activated cell-sorting. ATP-sensitive K+- channels in many different tissues are inhibited by sulfonylureas. The channels are thought to either be identical to, or else closely associated with, sulfonylurea receptors. The investigators studied clonal alpha-TC glucagonoma cells which derive from transgenic mice that express the SV40 T- antigen under the control of a glucagon promoter. The investigators found that these glucagonoma cells possess both sulfonylurea receptors and ATP- sensitive K+-channels that resemble those of B-cells. In addition, normal rate A-cells showed ATP-sensitive whole-cell currents which were inhibited by sulfonylurea and other hypoglycemic drugs. The investigators propose to characterize the ATP-sensitive K+-channels and glyburide receptors in normal rat A-cells, to assess the acute and long-term influence of glucose on the secretory and electrical responses of A-cells, to determine the role of ATP- sensitive K+-channels in glucagon release, to measure secretagogue-induced changes in the levels of ATP and free ADP in A-cells, and to generate a set of data on A-cell channels in order to apply the mathematical model of Chay to A- cell electrical activity. Besides the significance of the proposed work with respect to the regulation of glucagon release, the results are expected to influence current views of stimulus-secretion coupling in pancreatic B- cells.